Frequently Asked Questions on Caring for CDs and Their Longevity
by Christopher Dicks, Assistant Audio and Video Conservator, Library and Archives Canada, Music Division
Whether it is a collection of e-mail from your children, family photographs and films or recordings - both personal
and commercial - you want to store these digitized mementos properly so they can be enjoyed over the years.
This FAQ answers your questions about the CD as a long-term storage option, the life expectancy of a CD, the best
formats to use, how to store and clean CDs correctly, and how to determine the cause when your CD won't play
properly.
When CD-Rs are recorded, errors can result from the recording process itself. Fortunately, CD players or readers
have the ability to correct these errors. However, there is a limit to their correction capability. Therefore, you must
keep the amount of error as low as possible to ensure that your disc will play properly. In the past, 1x writing was
ideal, and many professionals chose to stay under 4x. Today, many CD-Rs have been designed to record at a faster
speed and may perform poorly at low speeds. Generally, recording a disc at around 4x produces the best quality
recording. Silver-manufactured CD-Rs enable a faster recording speed; therefore, a user might decide to record
faster to silver than to gold. However, the speed you choose must be in the range that your computer and
software can provide data to the CD burner and the range in which the burner can record the data.
Your recordings onto a CD-R can be unsuccessful. Data are read into a memory buffer before being sent to the
CD burner. A buffer underrun occurs when the memory buffer is empty, yet the CD burner is ready for more
data; therefore, the CD burning process fails. "Burnproof" technology solves the problem of buffer underruns by
commanding the burner to wait any time when there is not enough data in the buffer. The problem can also be
reduced or solved by fine tuning the buffer size settings in the CD-burning software and by using a faster
computer and a faster hard disk.
How should I handle my CDs?
Do not touch the surface of a disc with your bare hands - handle it by the edges and the
centre hole.
What should I use to label my CDs?
Mark only the non-recording surface of the CD (the clear inner hub portion of the disc). Use only solvent-free,
water-based, fine-tip markers, such as the Dixon Redisharp Plus. Their ink will not eat into a CD and destroy the
disc layers over time. Do not use adhesive labels because they can warp the disc as they contract, unbalance the
disc or chemically degrade the disc.
What are the best conditions for storing my CDs?
Store discs in regular-sized jewel cases in a vertical position when they are not being used. It is ideal to store CDs
in low light and cool, dry conditions that do not fluctuate widely. A good range for relative humidity is 20 to 50%
and for temperature, less than 23°C. If every element (materials, recording, formats, etc.) is of good quality and
stored within the proper ranges, then they are likely to last up to 100 years. However, if a disc is full of flaws
including poorer materials or if it is stored in hotter and more humid conditions than advised above, failures
may appear within five years. Thus, in less than optimal conditions, the best way to conserve your data is to
transfer (or "migrate") your files every five years to another medium such as a computer hard drive or a CD-R.
For longevity, is it best to store audio information on a CD-R as a .wav file or as an .mp3 file?
It is best to record your audio files
as a .wav file. An .mp3 file is a .wav file in which some data has been
discarded in order to reduce the file size. The computer chooses which
data to discard based on what the listener will least notice. You might be able to
“compress” an eroding.wav file into .mp3 format later on and end up with
a reasonably good .mp3. However, because the .wav file has already lost
so much when it was converted to .mp3,
a further loss from the aging of an .mp3 might be catastrophic.
If given the choice between recording, onto a CD-R, a .wav file into the
audio CD format (the same format as
the audio CDs you purchase) or recording it as a data file (like any other
file you would save), choose the data file.
When audio CD format files lose data, the player attempts to either insert
data from previous and following data,
or to mute the audio for a moment if there are too many consecutive errors.
Loss of data may translate into clicks
and pops when the CD is being played. However, a data file has a third
level of correction, which the processor
performs, that can provide extra protection against data loss and problems
signalled by muting, clicks and pops.
Test .wav files as soon as they have been recorded on a CD-R to determine
if anything has been lost.
How do I properly clean a CD?
The safest way to clean a CD or DVD is using a compressed air duster. Never use compressed solvent dusters.
The second safest cleaning tool is a soft, lint-free cloth. The third safest cleaning method involves using a soft,
lint-free cloth and distilled water to remove strongly attached debris. Soapy water (use mild dish soap) can remove
greasy debris such as fingerprints. If you use soap, rinse with clean, distilled water to remove any soapy residue. If
possible, avoid immersing the disc in water. Liquid solvents, which may erode the disc layers, and detergents are
not recommended.
When you wipe a CD, wipe from the centre of the disc outward in a radial direction (like spokes in a bicycle wheel)
to limit the amount of problematic scratching that may occur. A laser may be able to read "around" a radial scratch
on the disc surface, but a curved or spiral scratch could completely obscure parts of the disc and thus the data.
Why isn't my CD player or computer reading my CD?
Many things (for example, dirt or other residue
stuck to the surface) can disguise themselves as a CD drive
problem. Sometimes properly cleaning a CD will alleviate skipping and
even alleviate a lack of readability.
Always examine the surface of a CD before inserting it into the drive
or player.
However, do not rule out that a problem on a CD could be caused by your
CD drive. When a CD spins, it needs
to do so in a stable fashion, without wobbling. If the mechanism in the
drive allows the CD to wobble, then the data can at times be too far away to be read properly by the laser. This
wobble may cause the CD to skip or to be unreadable. Try to play your CD in someone else’s computer. If that
computer can read the disc, then you know that the problem could be due to your hardware.
A dirty lens in the CD drive can also cause a CD to be unreadable. A professional
technician should clean the CD
lens; although, with some advice and proper tools, you may be able to
do this yourself.
Your CD could also be unreadable because you are using an older CD drive.
Certain older drives can only read
older types of discs and may not be able to read the new recordable CDs
and CD-RWs that you or others have
created or bought. Newer drives may be more tolerant of errors or more
capable of correcting errors than are
older drives.
What is the difference between a DVD and a CD?
The information given for handling, labelling and cleaning a CD is also
applicable to Digital Versatile Discs (DVDs).
However the manufacturing and formatting specifications are different: some DVDs have two data layers on one
side while others have one layer on one side and another layer on the other side. Other DVDs have two data layers
on each side. CDs have one layer on only one side. DVDs have a greater storage capacity than CDs. This capacity
allows for better quality recordings.
The latest DVD player might be designed to read all pre-existing disc types including CD-R, but a player that
was designed before DVD was created cannot play a DVD. While it is possible to design the latest player to play
all digital disc types, most machines omit some disc formats. The consumer usually pays extra for each added
disc format. When purchasing a player, make sure it can play a wide variety of formats.
If you need professional conservation help, please contact
the Canadian Association of Professional Conservators:
CAPC
c/o Canadian Museums Association
Suite 400, 280 Metcalfe Street
Ottawa ON K2P 1R7
Tel.: (613) 567-0099
Fax: (613) 233-5438 http://www.capc-acrp.ca/index.htm
Additional Resources
For explanations and diagrams on how CDs are made and how they function, visit these Internet sites:
For further queries on various areas of conservation, please visit: Canadian Conservation Institute (CCI) Internet site (English and French): http://www.cci-icc.gc.ca/
